1. Field of the Invention
The present invention relates to a taking optical system for video shooting, and more particularly to a compact taking optical system for video shooting suitable for use in cameras provided with a solid-state imaging device.
2. Description of the Prior Art
In cameras (for example, video cameras or television cameras) that shoot an object by receiving a light beam incoming through a taking optical system by means of a solid-state imaging device (for example, a CCD (charge coupled device)) composed of an array of a plurality of light-receiving elements, a condensing microlens is provided on the incident-surface side of each light-receiving element so as to enhance its light-receiving efficiency. To increase the light-condensing ability of such condensing microlenses, conventional taking optical systems are so designed that the exit pupil is placed substantially at infinity (i.e. so designed as to be substantially telecentric toward the image side). In this structure, off-axial light beams enter the microlens from a direction approximately perpendicular to the incident surface of the light-receiving elements. This helps increase the light-condensing ability of the microlenses.
In recent years, to achieve more compact cameras, taking optical systems having short total lengths have been in demand. However, if a taking optical system is made shorter in total length, it is inevitable that its exit pupil comes closer to the image plane. This causes the microlenses disposed at the periphery of the image to receive off-axial light beams from oblique directions with respect to the incident surfaces of the light-receiving elements. As a result, the light-condensing ability of the microlenses is degraded at the periphery of the image, and thus the image shot by the solid-state imaging device suffers from uneven brightness between the central and peripheral portions thereof. As described above, in conventional taking optical systems, it is not possible to place the exit pupil substantially at infinity and simultaneously reduce the total length.